Conventional purified water dispenser units for use in homes or offices include a refrigerated bowl and a support for holding a bottle of purified water in an inverted position with its neck extending into the bowl. Water from the bottle fills the bowl to the level of the bottle neck at which stage the vacuum formed at the top of the bottle prevents further water flowing into the bowl. Where it is desired to provide both hot and cold water from a single dispenser unit, the bowl may be separated into upper and lower reservoirs by a horizontal plate, with the unrefrigerated water from the upper reservoir passing through a water heater before discharge from a separate hot water tap. When water is withdrawn from the bowl, the water level drops below the neck of the bottle and air enters the bottle. This relieves the vacuum in the top of the bottle and water flows into the bowl until the level again reaches the neck.
Water dispensers of this type require the purchase of bottles of purified water, which can be quite expensive and may be unavailable in remote areas. Furthermore, as the water in the bottle has been purified, all chlorine or other disinfecting agents have been removed and the water is unprotected against the growth of bacteria introduced by contaminated air bubbling through the water in the bottle.
Further disadvantages of the conventional purified water dispensers are the necessity of lifting and inverting full bottles of purified water onto the unit, and storage of both full and empty bottles. The storage of empty bottles creates a risk of contamination of the bottles, which are difficult to clean thoroughly through the small neck opening.
These disadvantages may be overcome by point-of-use filtration, in which tap water is purified shortly before use, thus retaining the chlorine in the water for as long as possible to minimise the likelihood of contamination. point-of-use filtration systems normally consist of a filter connected to the cold water plumbing, with a separate dispensing outlet connected to the filter outlet.
Australian Patent Application No. 57724/90 in the name of M. F. A. Robertson describes a point-of-use filtration unit for mounting on a conventional water dispenser unit. The unit comprises a filter which sits in and seals against the bowl and a container sitting above the filter with its neck inserted in the filter inlet. The container is filled with tap water through a lid at its top end. The water leaves the container through the neck, and is purified as it follows a tortuous path through the filtration medium and enters the bowl.
In the filtration unit of Patent Application No. 57724/90, the filter takes up a substantial volume of the bowl and thus reduces the volume of purified water held. This is particularly disadvantageous in units in which the bowl is separated into hot and cold water reservoirs.